Number-of-rotation detection device

ABSTRACT

The disclosed devices comprise a monostable multivibrator applied with periodic trigger pulses resulting from the rotation of the engine. If the engine has a speed of rotation less than a predetermined speed a voltage charged on a capacitor within the pulse period in the stable state of the multivibrator reaches a breakdown voltage of a Zener diode to produce an output from the latter. Otherwise the voltage across the capacitor does not reach the breakdown voltage to produce no output from the diode. Two capacitors may charge or discharge with different time constants in the stable state of the multivibrator while one of the capacitors is disabled in accordance with whether the actual speed is higher or lower than the predetermined speed.

atet 1 Saita 1 1 Apr. 17, I973 NUMBER-OF-ROTATHON DETECTION DEVICE [75]Inventor: Toshikazu Saita, Himeji. Japan {537755; Mitsubishi Iihki"KaBuhiki' K aisha,

Tokyo,.lapan [22] Filed: Apr. 26, 1971 [21] Appl. No.: 137,360

[30] Foreign Application Priority Data Aug. 1, 1969 Japan ..44/o0868Apr. 28, 1970 Japan ..45/36560 Aug. 21. 1970 Japan 45/8332! [52] US. Cl...324/l69, 324/161, 340/62, 340/263 [51] Int. Cl. ..G0lp 3/48 [58] Fieldof Search ..324/I6I, 169;

[5 6] References Cited OTHER PUBLICATIONS Marston, R. M.;Solid-State...; Radio-Electronics; April, 1970; pg. 33, 34, 36, 37, 38.

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Ernest F. KarlsenAIt0rney--Robert E. Burns and Emmanuel J. Lobato 5 7 ABSTRACT Thedisclosed devices comprise a monostable multivibrator applied withperiodic trigger pulses resulting from the rotation of the engine. Ifthe engine has a speed of rotation less than a predetermined speed avoltage charged on a capacitor within the pulse period in the stablestate of the multivibrator reaches a breakdown voltage of a Zener diodeto produce an output from the latter. Otherwise the voltage across thecapacitor does not reach the breakdown voltage to produce no output fromthe diode.

Two capacitors may charge or discharge with different time constants inthe stable state of the multivibrator while one of the capacitors isdisabled in accordance with whether the actual speed is higher or lowerthan the predetermined speed.

3 Claims, 11 Drawing Figures PATENTEB APR 1 71973 SHEET 1 OF 6 54 VOLTAGE DETECTOR CIRCUIT TIME DELAY CIRCUIT ROTATION SIGNAL GENERATORPATENTEI] APR 1 7 I975 SHEET 2 [1F 6 FIG. 3a

(A) TRIGGERING PULSE TO C|RCU!T 20 (B) COLLECTOR VOLTAGE 0F TRANSISTOR24 (C) VOLTAGE v ACROSS cAPAc|ToR46 TIME (D) OUTPUT FROM DETECTORc|Rcu|T50 F/G. 3b-

(A) TRIGGERING PULSE To CIRCUIT Z0 I| |lllTl E0 VZ O E G4. R .Z O T T RI O C T A s CP Rm v m E CA GS ER AS LT. T..O L LR OF CO CO VA m w E M T0 0 l U C mm C R R 0 T C PE TT UE OD.

PATENTED APR 1 7 I975 SHEET 5 BF 6 NUMBER-OF-ROTATION DETECTION DEVICEBACKGROUND OF THE INVENTION This invention relates to a device fordetecting the number of rotations per unit time of a rotary member, andmore particularly to a device for determining whether the number ofrotations or revolutions per unit time of a rotary member is greater orsmaller than a predetermined value.

There have been already proposed rotation detection devices of the typeincluding means for producing, as the rotation detection signal, a trainof electrical signals in accordance with the rotational movement of therotary member, and integration circuit means for integrating theelectrical signals with time to form an integrated voltage indicating ameasure of the particular number of rotations per unit time of therotary member. The integrated voltage provided by such an integrationcircuit means has been continuously changed in magnitude in response toa variation in the number of rotations per unit time of the rotarymember. Accordingly the rotation detection devices of the type as abovedescribed has been disadvantageous in that due to environment thereofsuch as a variation in the source voltage, a change in ambienttemperature etc., the integrated voltage changes in magnitude as well asthe system operation is performed with a time delay because the rotationdetection signal resulting from the rotational movement of the rotarymember is integrated by the integration circuit means. It is desirableto provide number-of-rotations detection devices including nointegration circuit means.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention toprovide a new and improved number-of-rotations detection device fordetermining whether the number of rotations per unit time of theassociated rotary member is greater or smaller than a predeterminedvalue thereof without the necessity of utilizing integration circuitmeans.

It is another object of the invention to provide a number-of-rotationsdetection device of the type as described in the preceding paragraph inwhich the actual value of the number of rotations or revolutions perunit time of the rotary member is selectively compared with a pluralityof predetermined values thereof.

It is still another object of the invention to provide anumber-of-rotations detection device of the type as above described inthe preceding paragraph for effecting the detection of a speed ofrotation of the rotary member with a hysteresis characteristic bycomparing the actual value of the speed of rotation with a pair ofpredetermined values thereof.

The invention accomplishes these objects by the provision of anumber-of-rotation detection device comprising, in combination, a rotarymember, a rotation signal generator circuit for periodically generatingrotation detection signals in accordance with the rotational movement ofthe rotary member, the rotation signals having a predetermined fixedduration, and a repetition period dependent upon the number of rotationsper unit time of the rotary member, a time delay circuit responsive tothe arrival of each of the rotation signals to produce a time delayedvoltage having a magnitude varying with time within the repetitionperiod,

and a voltage detector circuit having a threshold voltage and responsiveto the time delayed voltage in excess of the threshold voltage thereofto produce an output voltage indicating a measure of whether the numberof rotations per unit time of the rotary member is greater or smallerthan a predetermined fixed value.

The time delay circuit may preferably include a parallel combination ofa resister and a semiconductor diode connected to the output of therotation signal generator circuit and a capacitor connected in seriescircuit relationship with the parallel combination of the resistor anddiode.

In order to selectively detect a plurality of predetermined values ofthe number of rotations per unit time of the rotary member, the timedelay circuit may include a plurality of time delay networks connectedin parallel circuit relationship and different in time constant from oneanother, each of said time delay networks including a parallelcombination of a resistor and a semiconductor diode connected to theoutput of said rotation signal generator circuit, and a capacitorconnected in series circuit relationship with said parallel combinationof resistor and semiconductor diode; and one switching means connectedto each of said capacitors except for that capacitor being connected inthe time delay network having a maximum time constant to short circuitthe associated capacitor in accordance with the mode of operation ofsaid rotary member.

The time delay circuit may include a pair of time delay networksconnected in parallel circuit relationship and different in timeconstant from each other, each of said time delay networks to producethe time delayed voltage different in delay time from that produced bythe other time delay network, means for disabling one of said time delaynetworks in accordance with whether the number of rotations per unittime of the rotary member is greater or smaller than a predeterminedfixed value thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more readilyapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a block diagram of a device for detecting the number ofrotations or revolutions of a rotary member in accordance with theprinciples of the invention;

FIG. 2 is a circuit diagram of the details of the device shown in FIG.1;

FIGS. 30 and b are graphic representations of waveforms useful inexplaining the operation of the arrangement shown in FIG. 2;

FIG. 4 is a circuit diagram of a modification of the invention whereinthe actual number of rotations per unit times of a rotary member isselectively compared with a plurality of reference values thereof;

FIG. 5 is a circuit diagram of another modification of the inventionwherein the actual values of the number of rotations per unit time of arotary member is compared with a plurality of predetermined fixed valuesthereof.

FIGS. 60 and b are graphic representations of waveforms developed in thearrangement shown in FIG. 5;

FIG. 7 is a circuit diagram of a modification of the arrangement shownin FIG. 6; and

FIGS. 80 and b are graphic representations of waveforms developed in thearrangement shown in FIG.7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS While the invention isapplicable to a variety of rotary members it is particularly suitablefor use with internal combustion engines disposed on motor vehicles andtherefore it will now be described in conjunction with such an engine.

Referring to the drawings and FIGS. 1 and 2 in particular, it is seenthat a set of breakers contacts 10 and an ignition coil 12 are seriallyinterconnected in a well known manner for ignition in an internalcombustion engine. It is widely known that the contacts 10 are openedand closed in synchronization with the rotational movement of aninternal combustion engine involved although the engine is notillustrated in FIGS. 1 and 2.

The junction of the contacts I and the ignition coil 12 is connected toan input to a rotation signal generator circuit generally designated bythe reference numeral 20. As shown in FIG. 2, the generator circuit 20is formed of a monostable multivibrator comprising a pair of transistors22 and 24 including emitter electrodes connected together to a negativeterminal of a source of' direct current 14 and collecter electrodesconnected to the positive terminal of the source 14 through collectorresistor 26 and 28 respectively. The transistor 22 is in its normallyconducting state and includes a base electrode connected to thecollector electrode of the transistor 24 through a coupling capacitor 30and also to the positive terminal of the source 14 through a resistor 32while the transistor 24 is in its normally nonconducting state andincludes a base electrode connected to the collector electrode of thetransistor 22 through a coupling resistor 34 and also to the emitterelectrodes of both transistors 22 and 24. The base electrode of thetransistor 24 is further connected through an input resistor 38 to thejunction of the breakers contacts and the ignition coil 12. Themonostable multivibrator is of a conventional design.

Then the collector electrode of the transistor 24 is connected to a timedelay circuit generally designated by the reference numeral 40. As bestshown in FIG. 2, the time delay circuit 40 comprises a parallelcombination of a resistor 42 and a semiconductor diode 44 having one endconnected to the collector electrode of the transistor 24 and a timedelay capacitor 46 connected in series circuit relationship with theparallel combination of resistor 42 and diode 44 and also connected tothe negative terminal of the source 14. The resistor 42 and the diode 44form one part of a charging and a discharging circuit for the capacitor46 respectively.

The junction of the resistor 42 and the capacitor 46 is connected to avoltage detector circuit generally designated by the reference numeral50. The voltage detector circuit 50 is shown in FIG. 2 as consisting ofaZener diode 52 having a cathode electrode connected to the time delaycircuit 40 and an anode electrode connected to an output terminal 54.

The operation of the arrangement as illustrated in FIG. 2 will now bedescribed with reference to FIGS. 3a and b. Assuming that the associatedengine( not shown) is in operation, the breakers contacts 10 arerepeatedly opened and closed in accordance with the rotational movementof the engine. Each time the contacts 10 are open, a flow of currentthrough the primary winding of the ignition coil 12 is interrupted toinduce a reverse electromotive force across the primary winding as shownat waveform A in FIG. 312. Therefore the engine is ignited while atriggering pulse is applied to the rotation signal generator circuit 20to actuate it. That is, the circuit or monostable multivibrator 20 isput in its semistable state where the transistor 24 is conducting for apredetermined fixed time interval after which the transistor 24 isreturned back to its nonconducting state as well known in the art. As aresult, rectangular pulses having a predetermined fixed duration of t isdeveloped at the collector electrode of the transistor 24 as shown atwaveform B in FIG. 3a. During the conduction of the transistor 24 thecapacitor 46 in the time delay circuit 40 is fully discharged throughthe diode 44 and the now conducting transistor 24.

Then the monostable multivibrator or the signal generator circuit 20 isreturned back to its original state whereupon the transistor 24 isbrought into its nonconducting state. This permits the capacitor 46 tobe charged from the source 14 through the resistors 28 and 42. Thereforea voltage across the capacitor 46 is exponentially raised with respectto time. That is, the voltage V across the capacitor 46 may be expressedby V E(1 ewhere E is a voltage across the source 10, e is the base ofthe Napierian Logarithm and a is a time constant determined by themagnitude of the charging circuit for the capacitor 46. As shown atwaveform C in FIG. 3a, the voltage V across the capacitor 46 increasesuntil it drops to zero on the occurrence of the succeeding pulse or uponconduction of the transistor 24.

The voltage V across the capacitor 46 is then applied to the Zener diode52. If the voltage V does not exceed the Zener voltage V of the diode 52the latter provides no output at the output terminal 54. However if thevoltage V exceeds the Zener voltage V the diode 52 provides an outputvoltage of V V at the output terminal 54 as shown at waveform D in FIG.3a.

Therefore in case the engine has the number of rotations per unit timeless than a predetermined fixed value thereof, then a time intervalbetween each pair of adjacent spark ignition or a repetition period ofthe triggering pulses applied to the monostable multivibrator 20 is longenough to charge the capacitor 46 with a voltage in excess of the Zenervoltage of the diode 52 within that time interval with the result thatthe detector circuit 50 provides the output waveform C (see FIG. 3a) atthe output terminal 52.

On the contrary if the number of rotations per unit time of the enginebecomes higher than the predetermined value then the time intervalbetween the adjacent spark ignition decreases to such an extent that thecapacitor 46 is only charged with a voltage below the Zener voltage V ofthe diode 52 within each ignition time interval until it is dischargedthrough the succeeding operation of the monostable multivibrator 20 asshown at waveform C in FIG. 3b. Therefore the detector circuit 50provides a null voltage at the output terminal 54 as shown at waveform Din FIG. 3b. In FIG. 3b wherein the reference characters A and Bdesignate the respective waveforms corresponding to the waveforms A andB of FIG. 3a and developed with the number of rotations per unit time ofthe engine exceeding the predetermined value thereof.

From the foregoing it will be appreciated that the presence or theabsence of the output voltage at the output terminal 54 can determinewhether the number of rotations or revolutions per unit time of theassociated engine is lower or higher than a predetermined fixed valuethereof as long as the Zener or threshold voltage of the diode 52 isselected to correspond to the predetermined fixed value.

While the invention has been described in conjunction with a singlepredetermined fixed value of the number of rotations per unit time ofthe associated engine it is equally applicable to the case the number ofrotations per unit time of the engine is to be selectively detected fora plurality of predetermined fixed values thereof.

Referring now to FIG. 4 wherein like reference numerals designate thecomponents identical to those shown in FIG. 2, it is seen that the timedelay circuit 40 comprises a pair of parallel combinations eachincluding a charging resistor 42 or 42, a semiconductor dischargingdiode 44 or 44' and a capacitor 46 or 46 disposed in the same circuitrelationship as to the resistor 42, the diode 44 and the capacitor 46shown in FIG. 2 excepting that in FIG. 4 the capacitor 46 is connectedat one end to the junction of the resistor 42' and the capacitor 46rather than the negative terminal of the source 14. The resistors 42 and42 are different in magnitude of resistance from each other andconnected to the respective semiconductor output diodes 48 and 48 andthence to the Zener diode 52 in the detector circuit 50 with thejunction of the resistor 42' and the diode 48 connected to groundthrough a normally open switch 49. In other respects the arrangement isidentical to that shown in FIG. 2.

It is assumed that the switch 49 is maintained in its open positionillustrated in FIG. 4. During the operation of the associated enginetriggering pulses having a repetition period of z, are applied to themonostable multivibrator to conduct the transistor 24 for apredetermined fixed time interval of t as in the arrangement shown inFIG. 2. Therefore both capacitors 46 and 46 are fully discharged. Thenwhen the monostable multivibrator 20 is returned back to its originalstable state where the transistor 24 is in its nonconducting state, thecapacitors 46 and 46' begin to be charged from the source 14 through thecollector resistor 28 and their own resistors 42 and 42' with differenttime constants or time delays respectively. Thus a voltage across thecapacitor 46 will reach the Zener voltage of the Zener diode 52 in thevoltage detector circuit 50 upon a time interval of I timed out afterthe monostable multivibrator 20 has been returned back to its stablestate. Similarly, a voltage across the capacitor 46' will reach the sameZener voltage upon a time interval of t being timed out from the sametime point as does the time interval of t only for purpose ofillustration it is assumed that the time interval of t is longer thanthat of 1,

In this way the capacitors 46 and 46' are repeatedly charged anddischarged. If the number of rotations per unit time of the associatedengine(not shown) is low such that the repetition period t of therotation signals or triggering pulses applied to the monostablemultivibrator 20 is longer than the sums of the time interval i forwhich the multivibrator 20 is in its semistable state plus either of therise times t, and 1,; required for the voltages across the capacitors 4sand 46 to reach the predetermined value or Zener voltage of the diode52, that is, t,, (t,, t,,) (t 1, then the voltages across the capacitors46 and 46 become higher than the Zener voltage of the diode 52 or thepredetermined fixed voltage to be detected by the detector circuit 40.Therefore, the detector circuit 56 or the Zener diode 52 provides at theoutput terminal 54 an output voltage corresponding to the actual numberof rotations for unit time of the engine.

Then if the engine increases in the number of rotations per unit time sothat the relationship (t t,.,) t, (t t,.;) is held then the voltageacross the capacitor 46 is discharged through the succeeding conductionof the transistor 24 before it will reach the Zener voltage of the diode52. This results in the generation of a null voltage at the outputterminal 54. However, the voltage across the capacitor 46' exceeds theZener voltage of the diode 52. Accordingly, the Zener diode 52 is brokendown to produce at the output terminal 54 and output voltage dependentupon the actual number of rotations per unit time of the engine.

A further increase in the number of rotations per unit time of theengine causes the relationship z, (z t (t, t,,) to be held. As a result,both the capacitors 46 and 46 are caused to discharge before thevoltages thereacross reach the Zener voltage of the diode 52. This leadsto no output signal appearing at the output terminal 54.

Thus it will be appreciated that the time delay circuit 40 includes thetwo capacitors 46 and 46' and the associated charging circuits providinga pair of time delay networks different in delay time or time constantfrom each other and that whether the time interval 1, between each pairof rotation signals or the repetition period thereof is greater orsmaller than the sum of the time interval t for which the monostablemultivibrator 2th is in its semistable state and of the rise time t ofvoltage across the capacitor 46' can determine the predetermined valueof the number of rotations per unit time of the engine. It is noted thatthe predetermined value is determined by that time delay network smallerin time delay or time constant and including the capacitor 46'.

Assuming that the switch 49 is put in its closed position, the capacitor46 is shortcircuited to be disabled to perform the time delayingoperation. At the same time the diode 48' is reversely biased to exhibitno effect upon the detector circuit 50. Therefore that time delaynetwork longer in time constant and including the capacitor 46 isenabled to perform the time delaying operation thereby to determinewhether the time interval t, is greater or smaller than the timeinterval(t I This results in the determination of another predeterminedvalue of the number of rotations per unit time or a speed of rotation ofthe associated engine different from the speed of rotation for theswitch 49 in its open position.

if desired, more than two of the time delay networks connected inparallel to one another such as shown in FIG. 4 may be used toselectively determine a plurality of the numbers of rotations per unittime of the associated engine in accordance with the mode of operationthereof. In that event, individual normaliy open switches such as theswitch 49 shown in FIG. 4 are con nected across each of seriallyconnected capacitors expect for that capacitor providing a maximum delaytime. While the switch 49 is shown in FIG. 4 as being a mechanicalswitch, it is to be understood that if desired the switch 49 may besemiconductor switch.

While the invention has been described in terms of the time delaynetwork formed of the capacitor charging circuit it is to be understoodthat in practicing the invention the time delay network can be formed ofa capacitor discharging circuit which will be subsequently described inFIG. 5.

In FIG. 5 wherein like reference numerals have been employed to identifythe components identical or corresponding to those shown in FIG. 2 or 4,it is seen that the time delay circuit 40 includes a pair of paralleltime delay networks each formed of a semiconductor diode 44 and 44 adischarging resistor 42 or 42, and semiconductor output diode 43 or 48'serially connected in the named order. The junction of the diode 44 or44' and the resistor 42 or 42' is connected to ground through thecapacitor 46 or 46.

The diode 44 and 44 are connected at their anode electrodes to thecollector electrode of the normally conducting transistor 22 included inthe monostable multivibrator identical to that shown in FIG. 2 or 4. Theoutput diodes 48 and 48 are connected at their cathode electrodes to abase electrode of a transistor 52. The transistor 52 includes an emitterelectrode connected to ground and a collector electrode connected to thesource 14 through a collector resistor 54 to form the voltage detectorcircuit 50.

The collector electrode of the transistor 52 is also connected to atiming holder circuit generally designated by the reference numeral 60.The circuit 60 includes a series combination of a semiconductor diode 62and a discharging resistor 64 with the anode electrode of the diode 62connected to the collector electrode of the transistor 52. The junctionof the diode 62 and the resistor 64 is connected to ground through aholder capacitor 66.

As shown in FIG. 5, a switching circuit generally designated by thereference numeral 70 comprises a switching transistor 72 including abase electrode connected to the resistor 64 in the timing holder circuit60, an emitter electrode connected to ground and a collector electrodeconnected to the source 114 through a winding of a delay 74 connectedacross a semiconductor diode 76. A resistor 78 is connected across thebase and emitter electrodes of the transistor 72.

The collector electrode of the transistor 72 is also connected to a gatecircuit generally designated by the reference numeral 80. The gatecircuit 80 is shown in FIG. 5 as consisting of a semiconductor diode 32in- Cluding a cathode electrode connected to the collector electrode ofthe transistor 72 and an anode electrode connected to the anodeelectrode of one of the output diodes disposed in the capacitordischarging network having a greater time constant, in this case of thelower diode 48 as viewed in FIG. 5.

The operation of the arrangement illustrated will now be described inconjunction with FIGS. 6a and b. It is now assumed that the associatedengine (not shown) has the actual number of rotations per unit time or aspeed of rotation N less than a predetermined value N As in thearrangement shown in FIG. 2, the set of breakers contacts 10 responds tothe rotational movement of the engine to be repeatedly opened and closedto cause voltages of waveform A shown in FIG. 6a to be applied to themonostable multivibrator 20 to bring it into the semistable state for apredetermined fixed duration of t with a predetermined repetition periodof t,. In the semistable state the transistor 22 becomes nonconductingand the collector voltage thereof is high as shown at waveform B in FIG.6a. During the time interval of 1? the source 14 fully charges thecapacitors 46 and 46 through the collector resistor 26(see waveforms Cand D, FIG. 6a) and the respective diodes 44 and 44' and furthersupplies a base current to the transistor 52 in the detector circuit 50through the resistors 42 and 42' and the diodes 48 and 48 to bring it inthe conducting state. At the end of the time interval t or as soon asthe monostable multivibrator 20 is returned back to its stable state,the capacitors 46 and 46' are initiated to discharge with the differenttime constants as schematically shown at waveforms C and D in FIG. 6a.Under these circumstances, it is noted that the discharge current fromthe capacitor 46 having a lower time constant t for discharge isprincipally supplied through the resistor 42 and the diode 48 to thebase electrode of the transistor 52 continue to put it in the conductingstate as will be apparent hereinafter.

Upon the time interval 1,, having lapsed after the monostablemultivibrator 20 has been returned back to its stable state, thecapacitor 46' has fully discharged to put the transistor 52 in itsnonconducting state. This causes an increase in voltage at the collectorelectrode of the transistor 52 as shown at waveform E in FIG. 6a. Thetransistor 52 in its nonconducting state permits the timing holdercapacitor 66 to charge from the source 14 through the collector resistor54 and the diode 62 as shown at waveform F in FIG. 6a. Simultaneouslythe switching transistor 72 is applied with a base current from thesource 14 through the components 54, 62 and 64 to become conducting.Therefore the collector electrode of the transistor 72 is at a zeropotential as shown at waveform G in FIG. 6a and the winding of the relay74 is energized from the source 14 to put the relay in its operatingposition where the relay provides an output signal.

Each time the succeeding rotation signal is applied to the transistor 24the process as above described is repeated to maintain the transistor 52in its conducting state for the time interval of (t t after theapplication of that detection signal. By rendering the discharge timefor the holder capacitor 66 greater than the time interval of (t t theswitching transistor 72 continues to be in its "ON state with its basecurrent continuously applied thereto. Therefore the transistor 72 isheld in its ON state and hence the relay 74 is maintained in itsoperating state as long as the repetition period t, of the triggeringsignal is greater than sum of the conduction time t, of the transistor22 and the discharge time t of the timing holder capacitor 46. Thismeans that the system has an operating speed of rotation N equal to thereciprocal of the (t t As above described, the transistor 72 continuesto in its ON" state as long as the associated engine is rotating at aspeed N smaller than the N Accordingly the discharge current from thecapacitor 46 higher in time constant L for discharge flows through thegating diode 82 into the now conducting transistor 72 but not into thetransistor 52.

If the associated engine has its speed of rotation N higher than thepredetermined speed N then the arrangement of FIG. 5 has developedthereon waveforms A through G as shown in FIG. 6b corresponding towaveforms A through G as shown in FIG. 60. More specifically therepetition period t, is smaller than that t I so that the detectiontransistor 52 continues to be conducting because the base current iscontinuously applied to the base electrode thereof. Thus the switchingtransistor 72 remains in its OFF state without the base current appliedthereto and the relay 76 is in its inoperative position where itprovides no output. i

This transistor 72 in its OFF state causes the gating diode 82 to bereversely biased thereby to permit the time delay capacitor 46' tosupply a discharge current to the base electrode of the detectiontransistor 52. Since the discharge time t,, for the capacitor 46' ispreselected to be greater than the discharge time t for the capacitor46, the base current continues to be applied to the transistor 52 beforethe repetition period t, of the rotation signals becomes equal to theinterval of (t t,,). This means that the system has a reset speed ofrotation N equal to the reciprocal of the (t -l- 1,).

That is, the arrangement of FIG. 5 exhibits the hysteresischaracteristic having the operating speed of rotation N equal to l/ (t tand the reset speed of rotation N equal to l/ (t t,,), where the 2,, isgreater than the t While the arrangement of FIG. utilizes the dischargeof the capacitors to provide the time delayed voltages it is to beunderstood that for the same purpose it can be effectively modified toutilize the charge of the capacitors such as shown in FIG. 7.

In FIG. 7 wherein like reference numerals designate the componentsidentical or similar to those shown in FIGS. 2 or 5 it is seen that thenormally nonconducting transistor 24 in the monostable multivibrator isconnected to the .time delay circuit 40 identical to that shown in FIG.2 or 4 excepting that the capacitor 46 disposed in the smaller timeconstant network is connected to the gating diode 82. Also the voltagedetector circuit 50 comprises a normally nonconducting transistor 53connected to the Zener diode 52 and a normally conducting transistor 56directly coupled to the transistor 53. The transistor 53 includes a baseelectrode connected to the anode electrode of the Zener diode 52, anemitter electrode connected to ground and a collector electrodeconnected to the source 14 through a resistor 54. The transistor 56includes a base electrode connected to the collector electrode of thetransistor 53, an emitter electrode connected to ground and a collectorelectrode connected to the source M through a resistor 58.

The gating circuit 70 is shown in FIG. 7 as comprising the semiconductorgate diode 72 including the anode electrode connected to the junction ofthe capacitor 46 and the output diode 48 and the cathode electrodeconnected to a collector electrode of a normally nonconductingtransistor 84. The collector electrode of the transistor as is alsoconnected to the source 1 3 through a collector resistor 86 and theemitter electrode thereof is connected to ground. The transistor 8includes a base electrode connected to the collector electrode of theswitching transistor '72. In other respects the arrangement is identicalto that shown in FIG. 5.

It is assumed that the associated engine (not shown) is rotating at aspeed of rotation N below a predetermined speed of rotation N As in theprevious arrangements, the triggering pulses with a repetition period oft, (see waveform A, FIG. 8a) are successively applied to the monostablemultivibrator 20 to repeat the process as already described inconjunction with FIGS. 2 and and the waveforms B and C shown in FIG. 3a.Briefly the transistor 24 is put in its conducting state for apredetermined fixed time interval of t as shown at waveform B in FIG. 8aand as soon as the transistor 24 is returned back to its nonconductingstate the capacitors 46 and 46 beginning to charge with the respectivetime constants as schematically shown at waveforms C and D in FIG. 8a.Then the voltages across the capacitors 46 and 46 reach a predeterminedfixed voltage V to be detected by the detector circuit 40, in this case,the Zener voltage of the diode 52 after the lapse of time intervals of tand t from the returning back of the transistor 24 to its nonconductingstate or of the monostable multivibrator 20 to its stable staterespectively. At that time the diode 52 is broken down to supply a basecurrent to the transistor 53 to conduct it. This conduction of thetransistor 53 causes the transistor 56 to become nonconducting as shownat waveform E in FIG. 8a. Then the process as above described inconjunction with FIGS. 5, 6a and b are repeated to put the relay 74 inits energized state. In FIG. 8a waveforms F and G depict the voltageacross the capacitor 66 and the voltage at the collector electrode ofthe transistor.

As in the arrangement of FIG. 5, the discharge time for the holdingcapacitor 66 has been selected to be greater than the time interval of t-l- 2 Therefore the transistor 72 continues to be conducting andaccordingly the relay 14 is maintained in its operating state. Thus itwill be appreciated that the system has its operating speed of rotationN equal to the reciprocal ofthe (t -l-t On the other hand, thetransistor 8 in the gating circuit 86 is in its nonconducting statebecause the transistor 72 is maintained in its ON" state. This causesthe gating diode 32 to be reversely biased with the result the delaytime provided by the time delay circuit 40 is determined by the chargingtime I required for the capacitor 46 to be charged to the predetermined.This charging time t is smaller than the corresponding charging time tfor the other capacitor 46.

If the speed of rotation N is greater than the predetermined fixed speedof rotation N then the arrangement of FIG. 7 has developed thereon thecorresponding waveforms labelled the reference characters A, B, C, D, E,F, and G in FIG. 8b. In that event the repetition period or timeinterval T, between rotation signals is shorter than the time intervalof (t, r so that the output voltage from the time delay circuit 40 doesnot reach the threshold voltage V of the detector circuit 50. Thus thetransistor 53 remains nonconducting while the transistor 56 ismaintained in its conducting state. Thus the transistor 72 has appliedthereto no base current and remains in its OFF state thereby to maintainthe relay in its deenergized or inoperative state.

Also since the transistor 72 is in its OFF state the transistor 84disposed in the gating circuit 80 is in its conducting state to permitthe gating diode 82 to be forwardly biased. Therefore, the chargedvoltage on the capacitor 46 is clamped to the sum of the forward voltageacross the diode 82 and the saturated voltage of the transistor 84 andalways remains lower than the threshold voltage V of the detectorcircuit 50.

Even if the actual speed of rotation N decreases to the predeterminedfixed speed of rotation N the system remains in its mode of operationfor N N because the output from the time delay circuit 40 is below thethreshold voltage V of the circuit 50. A further decrease in speed ofrotation N will cause the repetition period I, to be equal to the timeinterval of (t I At that time the voltage across the capacitor 46reaches the threshold voltage V,,. Then if the repetition period t,becomes greater than the time interval of (t t,) a base current is againapplied to the transistor 53 to repeat the process as above describedresulting in the energization of the relay 74. Thus it will beappreciated that the arrangement shown in FIG. 7 has a reset speed ofrotation N equal to the reciprocal of the (2,, t,,). That is, thearrangement exhibits the hysteresis characteristic having the operatingspeed of rotation N l/ (t t and the reset speed of rotation NON: (t l tand N051: (t lt While the invention has been illustrated and describedin conjunction with a few preferred embodiments thereof it is to beunderstood that numerous changes and modifications may be resorted towithout departing from the spirit and scope of the invention. Forexample, the rotation detecting signals for the rotary member may beprovided by a reed switch operative to be open and closed in accordancewith the rotational movement of the rotary member or the engine. In thelatter event, the ignition coil, the breakers contacts and themonostable multivibrator are omitted. Also the voltage detector circuitmay be formed of a Schmitt trigger circuit. Further the invention isequally applicable to the detection of a speed of a vehicle. To thisend, one wheel of the vehicle driven by the associated engine may beutilized to produce the triggering pulses for applying the monostablemultivibrator.

I claim:

1. A number-of-rotations detection device comprising, a rotation pulsegenerator circuit for periodically generating pulses in dependence uponthe rotational movement of a rotary member, means in said pulsegenerator circuit causing said pulses to have a duration dependent uponthe number of rotations per unit time of the rotary number, means forintegrating each of the pulses for at least the duration of each pulseto produce an amplitude dependent on the pulse duration and forreturning the amplitude to zero value, means for detecting whether theamplitude of the integrated pulses is above or below a predeterminedvalue to determine whether the number of rotations per unit time of therotarg member is above or below a predetermined value, sat means forintegrating lncludmg a plurality of pulse generator means for generatinga plurality of sloped pluses different in rate of change in voltage fromone another during the periods of the first-mentioned pulses, aselection switch for selecting sloped pulses, and voltage detectionmeans receptive of the sloped pulses selected by the selection switch toproduce an output in response to the applied sloped pulses having avoltage exceeding a predetermined magnitude.

2. A number-of-rotation detection device as claimed in claim 1, whereinthe selection switch comprises means controlled in response to anoperating state of an associated internal combustion engine.

3. A number-of-rotation detection device as claimed in claim 1, whereinthe selection switch means is controlled in response to an output fromsaid voltage detection means.

1. A number-of-rotations detection device comprising, a rotation pulsegenerator circuit for periodically generating pulses in dependence uponthe rotational movement Of a rotary member, means in said pulsegenerator circuit causing said pulses to have a duration dependent uponthe number of rotations per unit time of the rotary number, means forintegrating each of the pulses for at least the duration of each pulseto produce an amplitude dependent on the pulse duration and forreturning the amplitude to zero value, means for detecting whether theamplitude of the integrated pulses is above or below a predeterminedvalue to determine whether the number of rotations per unit time of therotary member is above or below a predetermined value, said means forintegrating including a plurality of pulse generator means forgenerating a plurality of sloped pulses different in rate of change involtage from one another during the periods of the first-mentionedpulses, a selection switch for selecting sloped pulses, and voltagedetection means receptive of the sloped pulses selected by the selectionswitch to produce an output in response to the applied sloped pulseshaving a voltage exceeding a predetermined magnitude.
 2. Anumber-of-rotation detection device as claimed in claim 1, wherein theselection switch comprises means controlled in response to an operatingstate of an associated internal combustion engine.
 3. Anumber-of-rotation detection device as claimed in claim 1, wherein theselection switch means is controlled in response to an output from saidvoltage detection means.